1. Field of the Invention
The present invention relates to the field of communications networks. More particularly, the present invention pertains to a method and system for providing network connectivity and mobility for a roaming client.
2. Related Art
In a wireless communication network environment, a “client” node is associated to an “Access Point” (AP) in order to access a backbone or distribution communication network. The AP can be a hub or a switch in a wired network and the AP is commonly known as a Wireless Access-Point in a wireless LAN (Local Area Network). An AP has to be successfully connected to the backbone network before the client is able to log on to the backbone network.
FIG. 1 shows a communication network 50 in the prior art that shows a wireless communication network that is coupled to a backbone network via a wired connection, such as Ethernet. The wireless network consists of at least one access point (AP) connected to the wired network infrastructure and a set of wireless end stations, or clients, that are associated with that particular AP. The AP acts as a bridge between the wired and wireless networks. Additionally, a subnetwork, or subnet, may contain one or more APs along with their respective associate clients.
FIG. 1 shows two access point wireless networks, AP-A network 110 and AP-B-network 150, in a communication network 50. In AP-A network 110, an access point AP-A 112 is wired to the backbone network 130. Various clients, A-1 114, A-2 116, on up to A-n 118 are connected to AP-A through a wireless connection to form AP-A network 110. Similarly, in AP-B network 150, an access point AP-B 152 is wired to the backbone network 130. Various clients, B-1 154, B-2 156, and on up to B-n 158 are connected to AP-B 152 through a wireless connection to form AP-B network 150. The network 50 could support and operate with more than two AP networks.
Additionally, two or more APs, such as AP-A 112 and AP-B 152 may form a subnetwork, where the subnetwork operates with a common network mask and common gateway. Moreover, individual APs may be part of different subnetworks. For example, in FIG. 1, AP-A 112 may be part of sub-network N1 with network mask M1 and Gateway G1, and AP-B 152 may be part of sub-network N2 with network mask M2 and Gateway G2.
An access point acts as the base station for the wireless network, aggregating access for multiple wireless end stations or clients onto the wired network, such as the backbone network 130 in FIG. 1. Each AP communicates with the clients over the wireless medium that is associated with that AP. For example, AP-A 112 communicates with its associate clients A-1 114, A-2 116, and on up to A-n 118. The AP communicates with other APs and other nodes on the network 50 via the backbone network 130. A function of the AP, among many others, is to relay network traffic from its associated clients. The destination of this traffic may be another end station in the same, or different, AP network, or the destination may be a node on a wired LAN (such as ethernet) connected to the backbone network. The AP provides this relaying function for end stations simultaneously.
A problem arises where a client, such as a notebook with networking capabilities, roams from a first subnet to a second subnet. For example, a user operating the client notebook may bring the client notebook to another building location, that is located in a different subnet, for a meeting. The mobility of the client requires the connection/disconnection or association/disassociation to occur between different APs from time to time. The challenge here is to have the various APs and the client communicate intelligently such that the network connection appears to be radically simple to the user throughout the client's mobility. When a client moves from a first subnet to a second subnet, its IP (Internet Protocol) address being used in the previous subnet might not be valid in the second subnet.
Additionally in the wireless LAN world, a client may have to associate with another AP in a second subnet even though the client hasn't physically moved. This may be due to a failure of the association with the original or first AP. The connection status of the AP to the backbone is commonly not reported to the user when the AP-backbone connection fails, leaving the user uninformed of its loss of transmission.
There are several possible scenarios where a client may experience loss of connection from the backbone network 130. For example, looking at FIG. 1, assume that we have a client A-2 116 and several AP's, namely AP-A 112, AP-B 152, on up to AP-n (not shown). Further, assume that AP-A 112 along with AP-A network 110 belong to subnetwork N1 (not shown) with network mask M1 and Gateway G1, and AP-B 152 along with AP-B network 150 belong to subnetwork N2 (not shown) with network mask M2 and Gateway G2 as in FIG. 1.
First, if the client A-2 116 roams or disconnects/reconnects with its associated AP-A-112, there may be a loss of connection from the backbone network 130. Initially, the client is within the service area of AP-A 112. After boot up, the client will send out a DHCP (Dynamic Host configuration Protocol) request and receive one IP address IP1 associated with subnet N1, network mask M1, and Gateway G1. Subsequently, the client may move around, roam to or connect with another AP in another subnet, such as AP-B 152 in subnet N2. If the client is not aware of the switch to AP-B 152 and uses the same IP1 which is not within subnet N2, Gateway G2 will not forward packets sent by the client whose default gateway is G1. In most cases, N1 and N2 are different, that is AP-A 112 and AP-B 152 reside on different subnets.
Second, in the above example, when AP-A 112 loses its backbone connection, a resulting loss of connection occurs between the client A-2 116 to the backbone connection 130. In general, if an AP's link to the backbone is lost, its connected or associated clients will have no knowledge of such network failure and the associated clients will have to wait for the network administrator to pinpoint the problem and fix it. If it's a wireless AP, during this downtime period, any new wireless client that roams to this AP will not be able to connect to the backbone network even though the client successfully associates with the AP. Additionally, the new wireless client would not know that there is not a connection between the AP and the backbone connection 130.
Thus, there is a need for a more efficient system for monitoring connectivity to a communication network, especially when a client roams throughout a communication network from one subnet to another subnet.